There are two sides to PPC advertising: the advertiser side and the publisher side... Advertisers are obviously those who run the ads, while publishers are those who host them on their sites and receive money for each click. Which are you looking to do?
before you join the ppc you must search first if they're not a scam so that it will not waste your time and effert.
Some Ad networks pays you for joining like bidvertiser. Adbrite is good for an advertiser. Chitika , Bidvertiser and Pocket Cents are good for a publisher
Pick an ad network, register, create your campaign and fund your account. then start your test ad ( track/tweak ). There are many PPC networks that you can join. When you choose one, make sure that you understand their rules very well before you do anything else. Good luck,